1. Technical Field
The present invention relates to an image processing apparatus for processing image data on the basis of the obtained data, an image reading apparatus having the image processing apparatus, an image forming apparatus having the image processing apparatus, an image processing method for image data on the basis of the obtained data, and a recording medium in which a computer program for processing image data on the basis of the data obtained in a computer.
2. Description of Related Art
Electronization of information has been largely proceeded as well as printers, copying machines and multi-function printers have been widely spread these days. This results in increasing cases where document data is created on the basis of a document of a sheet-shaped recording medium (hereinafter simply referred to as a document) so as to deliver the created document data.
Meanwhile, as a method for adding additional data to a printed matter, a method using a two-dimensional code has been widely spread. An example of the two-dimensional code is a QR (Quick Response) code. Cellular phones now widespread among a large number of people are equipped with a function to read a QR code. Also, a function to create a QR code is provided as a function of a cellular phone in some cases and is provided as software for a computer in other cases.
A so-called data embedding technology for embedding additional data into a document while taking the layout into consideration without making the human eye feel the deterioration of the image quality so much without requiring an area to which a code is added separately, unlike the case where a QR code is added to a document (printed material), has been developed. As one such example, microgradation for displaying additional binarized data as a predetermined pattern having a difference in the density in the design pattern, which is a technology for embedding additional data into a design pattern that is the page background of a document, has been disclosed (Kensuke Ito and 4 others, “Paper Document Security” Fuji Xerox Online Technical Report, searched on Nov. 29, 2008, http://www.fujixerox.co.jp/company/tr/15/download/pdf/t—4.pd f).
Meanwhile, a text hiding technology using visible watermark information in a halftone screen (hereafter, in this invention, we express visible watermark information in a halftone screen technology as visible watermark information technology, for short.) has been known as a method for checking the unauthorized copying of a document. The text hiding technology using visible watermark information in a halftone screen uses the fact that printers have higher resolution than scanners. In further detail, as shown in FIG. 21A, a hidden text “Copy Strictly Prohibited” is printed with such a resolution that can be read by scanners, and at the same time, a pattern (visible watermark information in a halftone) with such a resolution that cannot be read by scanners is printed on the entire printed surface of the recording medium for the purpose of making it difficult for the human eye to perceive the above described hidden text “Copy Strictly Prohibited” and thus, the document is complete. As a result, when this document is copied, as shown in FIG. 21B, the visible watermark information in a halftone printed in the document cannot be read by the scanner, and therefore, is not copied so that only the hidden text “Copy Strictly Prohibited” having such a resolution that can be read by the scanner is copied, and thus, copying can be checked.
The visible watermark information technology is a technology for embedding a subtle change that cannot be perceived by the human eye when the document is outputted so that the information can be detected if necessary.
In the following, an another example of the visible watermark information technology is described. FIGS. 22A and 22B are diagrams for illustrating visible watermark information. The visible watermark information “x” characters are embedded in the documents in FIGS. 22A and 22B with a subtle difference in the resolution from the visible watermark information in a halftone, which is difficult for the human eye to perceive. As can be seen from the diagrams showing an enlargement of each visible watermark information “x” character and its periphery, the visible watermark information “x” character is made up of dots with a great number of lines (resolution being high), while the visible watermark information in a halftone in its periphery is made up of dots with a small number of lines (resolution being low) in FIG. 22A. The visible watermark information “x” character is made up of dots with a small number of lines, while the visible watermark information in a halftone and its periphery is made up of dots with a great number of lines in FIG. 22B. The areas with a small number of lines can be detected by scanners, while the areas with a great number of lines cannot be detected by scanners. Accordingly, the visible watermark information “x” characters having such a resolution that cannot be read by scanners are white in the copy in the case where the document in FIG. 22A is copied, while only the visible watermark information “x” characters having such a resolution that can be read by the scanner are copied in the case where the document in FIG. 22B is copied, and thus, copying can be checked.